Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $84.89   7.705%   $91.4308   $91.43   $91.45   $91.40  
  Purchase #2 $129.60   11.598%   $144.631   $144.63   $144.65   $144.60  
  Purchase #3 $145.42   5.287%   $153.1084   $153.11   $153.10   $153.10  
  Purchase #4 $116.52   10.818%   $129.1251   $129.13   $129.15   $129.10  
  Purchase #5 $222.31   10.170%   $244.9189   $244.92   $244.90   $244.90  
  Purchase #6 $7.92   11.514%   $8.8319   $8.83   $8.85   $8.80  
  Purchase #7 $192.42   13.612%   $218.6122   $218.61   $218.60   $218.60  
  7 purchase totals = $899.08       $990.6583   $990.66   $990.70   $990.50